In-mold decoration processes involve decorating objects as they are formed, in mold, of a heated plastic material being injected into a mold cavity. Usually a tape or strip of a decorating or protective material is automatically or manually advanced, pre-fed and positioned in the mold cavity at each molding cycle, interfacing therein with the plastic material as it is filled into the mold cavity, under heat and pressure. As the object is formed, the decorating material forms on the surface of the object and becomes an integral and permanent part of the object, through thermal transfer in the in-mold decoration process. Other molding processes such as thermal forming, blow molding and compression molding or stamping may also be used for the transfer of the decorating or protective material. Sometimes the process may also be called in-mold labeling or in-mold coating, and the transferable protective material may be called a thermal transfer overcoat or durable coat layer.
The decoration tape or strip usually comprises a carrier layer, a release layer, a durable layer, an adhesive or tie-coat layer and also a layer of decorative designs (metal or ink). After the injection molding transfer, the carrier layer and the release layer are removed, leaving the durable layer as the outmost layer. The durable layer serves as a protective layer with scratch resistance, mar or abrasion resistance and solvent resistance to protect the decorative designs and also the molded object. The adhesive layer is incorporated into the decoration tape or strip to provide optimum adhesion of the decoration tape or strip to the top surface of the molded object.
However, the currently available decoration tape or strip has many disadvantages. For example, when the carrier and release layers are removed, the durable layer cannot be cleanly separated from the release layer, especially at the edges of the molded object. The residual durable layer at the edges has to be removed manually. As a result, fragments of the residual durable layer inevitably generate debris which not only causes contamination to the production environment but also reduces the production yield. This problem is even more pronounced when the molded object has a small hollow structure, such as a speaker and ear pieces of a cell phone cover.
The problem is most likely caused by poor fracture characteristics of the decoration tape or strip and/or the inappropriate balance between the cohesion strength of the durable and adhesive layers and the adhesion strength at the interface between, such as the durable and release layers, the durable and ink layers, the durable and metal layers, the adhesive and metal layers, the durable and adhesive layers and/or the adhesive layer and the molding plastic material.